Dielectric heating/drying systems are known and are currently in use or have been proposed for use in agriculture, polymer manufacture, pharmaceuticals, bulk powder, food processing, wood products, building materials, and other industries. One of the key industries using these dielectric heating/drying systems is the wood products industry and the present invention will be described particularly with respect to the wood products industry although the invention, with suitable modifications where required, may be applied in the other industries in which dielectric heating/drying is to be performed.
In dielectric drying systems (particularly those for drying wood of the type described in U.S. Pat. No. 3,986,268 issued Oct. 19, 1976 to Koppelman), it is conventional practice for the lumber to be moved into the drying chamber, at least one power electrode that will emit electromagnetic energy and a grounding electrode to complete the circuit are positioned near or in contact with the load. After the load has been positioned in the kiln, the kiln chamber is closed and the drying process is commenced by applying a negative pressure in the chamber and applying power (energy) to the load through the power and grounding electrodes. U.S. Pat. No. 5,942,146 issued Aug. 24, 1999 to Blaker et al. (the disclosure of which is incorporated herein by reference) teaches that shaping of the electrode connectors, (elements carrying the power to the load) is important and describes the minimum curvature required for improved operation.
The electrodes used in dielectric drying systems generally have a planar surface facing the load. One theoretical system to obtain optimum RF uniformity within the load requires that the power electrode have an infinitely long and infinitely wide planer surface; obviously, this is not practical.
It is Applicant's understanding that an experiment incorporating small wings or flanges at the sides of the electrodes and projecting on opposite sides of the load was previously performed and while an effect was observed the effect was of minimal practical significance in comparison to the Applicant's current invention.